This invention relates to a flue gas scrubbing system for removal of sulfur dioxide from flue gases of a steam generator, and in particular to an arrangement which more effectively utilizes the limestone of such a system. Flue gas scrubbing systems of the type contemplated herein and the chemistry involved are described in a paper entitled "Lime/Limestone Air Quality Control Systems: Effect of Magnesium On System Performance", by Messrs. Frabotta and Rader and presented at the Winter Annual Meeting of the ASME during Dec. 5-10 of 1976. The prior art systems in general suffer in that a portion of the freshly added limestone is conveyed to waste along with disposal of the unwanted waste products.